What if I don't reply to my girlfriend's information in time? I forgot to mute my cell phone. She told me it was urgent.

You should apologize to your girlfriend at the first time, ask her for forgiveness, and be sure to explain to her why you didn't reply to her message in time.

Apologize directly to your girlfriend for losing money. Forgive me. I really didn't mean to, and I really didn't find out that you sent me a message because my phone was silent.

Seeing your news, I did reply to you at the first time. It's not that I don't care about you, nor that I deliberately delayed.

And promise your girlfriend that this will never happen again, and the phone will never be muted again.

No matter what you say in the future, I will reply as soon as possible, so please forgive me this time. It won't happen again.